(1) Field of the Invention
The present invention concerns a microporous paper filter for particulates.
More in detail, the invention concerns a microporous paper filter for particulate, having large volume surface to filter the particulate released together with the exhaust gases of internal combustion engines, such as the Diesel cycle engines.
(2) Description of Related Art
The general problem of environmental pollution, produced not only by the internal combustion engines, in particular the Diesel cycle engines, but also through different sources, such as, for example, the burners of the heating systems, is mainly centered on the particulate comprising unburned carbon particles which, when of small particle size, normally smaller than 10 microns, represent a great danger for the health of the inhaling person.
The atmospheric conditions, the traffic increase in cities and the increase of the Diesel cycle engines, have greatly increased the problem, and drastic measures for the traffic limitation were adopted in urban areas.
Various solutions have been proposed to remedy a continuously worsening pollution situation, operating according to different principles.
Among the filtering systems proposed, there are those called self-regenerating, for example a filter is well known, consisting of a device comprising a section containing a catalyst which generates nitrogen dioxide (NO2), followed by a section consisting of a ceramic filter capable of retaining the particulate.
When this filter reaches the temperature of 250° C., NO2 triggers the combustion of the carbon particles trapped in the filter, thus preventing the progressive obstruction.
But the above-described device has some limitations:                gas oil must not contain sulfur, otherwise the catalyst is poisoned;        the device functioning is linked to the exhaust gas temperature;        the combustion ashes of the lubricating oil cannot be eliminated from the particulate filter, which, therefore, is progressively obstructed;        the NO2 production can represent a danger for the environment;        it is not easy to verify the efficacy of the system during the running of time.The non negligible realization and installation costs are to be added to the above drawbacks.        
This solution did not have, for the above reasons, great success for the solution of the environmental pollution problem due to exhaust gases.
The general object of the present invention is, therefore, to produce a microporous paper filter for particulate, having high volume surface, which results fairly durable.
Another object of the present invention is to produce a microporous paper filter of particularly reduced dimensions, which can be housed into a container, of economical production and simple installation and substitution.
Another object of the present invention is to produce a filter consisting of a microporous paper suitably selected, capable of retaining the particulate emitted together with the discharge gases of internal combustion engines, particularly Diesel cycle engines, having dimensions lower than 10 microns.
Another object of the present invention is to produce a filter which allows not to disperse the particulate, separated from the exhaust gases, in the atmosphere.
A further object of the present invention is to produce a filter which does not present an appreciable pressure drop for the gases which go through it, therefore which does not cause significant counter-pressures in the exhaust.
These and other objects according to the present invention are achieved by a microporous paper filter for filtering particulates.